Re: How can I start SELinux play machine ?

[Daniel J Walsh <dwalsh@xxxxxxxxxx>]

On 02/18/2010 04:44 PM, Dominick Grift wrote:

On 02/18/2010 10:17 PM, Shintaro Fujiwara wrote:
  

Hi, I 'm ready to start SELinux server in my office first time, and I
want to persuade everyone how safe the SELinux server is.

How can I demonstrate administrators and my boss the advantage of
SELinux comparing other servers?

SELinux play machine hit me but is too far or should I just
demonstrate in a certain ocassion for certain purpose?
    

It depends a bit on your distro and policy model.

But generally you can demonstrate how TE enforces integrity for targeted
system daemons.

If you use strict policy you can also enforce integrity for user
processes. You can also demonstrate role based access control.

You can demonstrate how MCS can be useful to restrict processes access
to objects.

If you use MLS model you can demonstrate enforcement of confidentiality.

I never actually connected to play machine but i gather it mapped the
root Linux login to the user_u SELinux user.

There are a lot of ways to demonstrate SELinux. You could restrict a
simple hello world shell script and shows what happens if you extend the
script to make it do something it is not intended to do.

Same goes for webapplications. You could write a webapp and make it do
something that SELinux policy does not allow it to do.

Generally TE tries to prevent privilege escalation. It restricts processes.

  

Thanks in advance.

    

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Simple demonstration in Fedora 12.  Create a script.

cat > /usr/bin/showshadow << _EOF
#!/bin/sh
id
cat /etc/shadow
_EOF

chmod +x /usr/bin/showshadow

showshadow
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel) context=staff_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
root:*:::
bin:*:14043:0:99999:7:::
daemon:*:14043:0:99999:7:::
adm:*:14043:0:99999:7:::
lp:*:14043:0:99999:7:::
sync:*:14043:0:99999:7:::
shutdown:*:14043:0:99999:7:::
halt:*:14043:0:99999:7:::
mail:*:14043:0:99999:7:::
news:*:14043:0:99999:7:::
uucp:*:14043:0:99999:7:::
operator:*:14043:0:99999:7:::
games:*:14043:0:99999:7:::
gopher:*:14043:0:99999:7:::
ftp:*:14043:0:99999:7:::
nobody:*:14043:0:99999:7:::
vcsa:!!:14043:0:99999:7:::
distcache:!!:14043:0:99999:7:::
nscd:!!:14043:0:99999:7:::
tcpdump:!!:14043:0:99999:7:::


# sandbox showshadow
uid=0 gid=0 groups=0,1,2,3,4,6,10 context=staff_u:unconfined_r:sandbox_t:s0:c512,c625
cat: /etc/shadow: Permission denied

To see the error message

# ausearch -m avc -ts recent
----
time->Thu Feb 18 17:03:36 2010
type=PATH msg=audit(1266530616.620:1997): item=0 name="/etc/shadow" inode=5688120 dev=fd:01 mode=0100400 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:shadow_t:s0
type=CWD msg=audit(1266530616.620:1997):  cwd="/tmp"
type=SYSCALL msg=audit(1266530616.620:1997): arch=c000003e syscall=2 success=no exit=-13 a0=7fff6bb88798 a1=0 a2=7fff6bb88120 a3=a items=1 ppid=26934 pid=26938 auid=3267 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts0 ses=3 comm="cat" exe="/bin/cat" subj=staff_u:unconfined_r:sandbox_t:s0:c512,c625 key=(null)
type=AVC msg=audit(1266530616.620:1997): avc:  denied  { open } for  pid=26938 comm="cat" name="shadow" dev=dm-1 ino=5688120 scontext=staff_u:unconfined_r:sandbox_t:s0:c512,c625 tcontext=system_u:object_r:shadow_t:s0 tclass=file

grep shadow /var/log/messages
Feb 18 17:03:42 localhost setroubleshoot: SELinux is preventing /bin/cat "open" access on /etc/shadow. For complete SELinux messages. run sealert -l 95108dbb-8254-4a00-886d-028bafa4996a

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